MRSA is drug-resistant Staphylococcus aureus against which antibiotics including methicillin have been ineffective. The emergence of MRSA was first reported in 1961 in England, and thereafter MRSA spread rapidly across the world. Nowadays MRSA comprises 50-70% of Staphylococcus aureus isolated in medical facilities, and is rampant in hospitals. Health care providers and patients are easy to infect with MRSA by contact within medical facilities. Usually healthy persons become just carriers when infected with MRSA because MRSA itself is a variant of Staphylococcus aureus and has low pathogenicity. On the other hand, when aged persons with reduced immunity, patients with immunodeficiency, post-operative patients, or patients having an intubated catheter in the trachea or a blood vessel are infected with MRSA, it proliferates within the body to cause various infectious diseases such as pneumonia, enteritis, septicemia, endocarditis, and meningitis. In the West and in Japan where medical care is highly developed, MRSA infections are regarded as one of the most serious infections in medical facilities, and require various countermeasures for prevention of its infections.
Since there is no apparent difference in symptoms and progress between MRSA infections and other bacterial infections, MRSA infections are very difficult to distinguish by general clinical findings and laboratory test values. The diagnosis is confirmed by identification of MRSA by microbiological examination. For the treatment of MRSA infections, the administration of antibacterial agents is effective in combination with symptomatic treatment. However, it is necessary to use special antibacterial agents such as vancomycin and teicoplanin which are effective against MRSA because MRSA is resistant to common antibacterial agents. When using these agents, the dosage and period for administration should be limited to the minimum in order to prevent the emergence of new resistant strains. Currently the antibacterial agents which are used for MRSA infections require rather long period of time until they exhibit a desired effect and therefore rapid recovery of the patients cannot be expected.
In contrast to the above-described situation, a depsipeptide antibiotic named WAP-8294A2 has been developed as a promising antibacterial agent (Patent Document 1). WAP-8294A2 has a relatively narrow antibacterial spectrum, and it has remarkably strong antimicrobial activity against MRSA and can kill MRSA in a short period of time bactericidally. Therefore, WAP-8294A2 is considered to be effective especially against acute exacerbation of MRSA infections because of its strong antibacterial action, and it is expected to be a therapeutic agent which can contribute to rapid recovery of patients in critical condition due to MRSA infections.
Patent Document 1: Japanese Patent No. 3339235